lively (12), 50 to 100 years before any useful antituberculosis drugs were discovered and several decades before any organized antituberculosis programs were started. Furthermore, in some relatively recent studies it has been found that, contrary to prevailing theory, tuberculosis does not necessarily occur under crowded conditions. Under some circumstances at least it occurs more frequently in people who are socially isolated. In a careful study conducted in Britain (13), all the families living in a city were X-rayed to determine the prevalence of tuberculosis in relationship to an index of crowding (derived by dividing the number of people in a household by the number of rooms in the house). Although the prevalence varied a great deal with social class, within each social class no relationship between the crowding index and tuberculosis prevalence was found. In fact, lodgers who were living alone in the houses had a tuberculosis rate some three to four times higher than family members even though the lodgers were, by definition, living in uncrowded conditions. Similar results were found in a study in the United States (14). It was found that tuberculosis was occurring most frequently in people living alone in a single room and not in those living under the most crowded conditions. The Higher Rates of Disease Reported under Crowded Conditions Although there can be little doubt that outbreaks of disease, particularly acute upper respiratory disease, are more common under the crowded conditions of military training camps, for example, than under less crowded conditions, there is considerable doubt that such outbreaks can be ascribed solely to the physical fact of increased crowding. In recent years intensive study of outbreaks of upper respiratory infection in recruits in military training camps have indicated that the agent responsible is usually the adenovirus IV. The orthodox explanation for such outbreaks holds that they result from the herding together of large numbers of susceptible young men with a few infected individuals and that crowded conditions facilitate the spread of the agent. Such an explanation, however, fails to account for some of the known facts. For example, the same agent, the adenovirus IV, is widespread in civilian populations, but even under conditions of crowding, as in colleges and schools, has never been implicated in an outbreak of upper respiratory infection. Furthermore, the permanent staff of the military installations, living under the same crowded conditions as the recruits, are not involved in such outbreaks. Finally, immunization experiments against adenovirus IV have been conducted under appropriate double-blind conditions. The immunized companies displayed a reduction in the number of cases ascribed to adenovirus IV, but they experienced just as much upper respiratory illness as had the control companies, now due to a different agent—adenovirus VII.